FIG. 18 is an overall configuration diagram illustrating a conventional vacuum measurement device measuring the density (pressure) of a gas remaining inside a vacuum device, and FIG. 19 illustrates a gauge head including an ion source. Further, the gauge head shown in FIG. 19 is also a gauge head of a vacuum gauge called an extractor vacuum gauge.
In FIGS. 18 and 19, an ion source 3′ is constituted of three electrodes, that is, a grid 10′, an electron source 20, and an ion extractor 30′. In some cases, only two electrodes, that is, a grid 10′ and an electron source 20 may be called an ion source. However, in this invention, three electrodes, that is, a grid 10′, an electron source 20′, and an ion extractor 30′ are called the ion source 3′.
In FIG. 19, a gauge head (denoted by the reference numeral 2′ of FIG. 18) of an ionization vacuum gauge is configured by additionally providing an ion collector 40′ capturing an ion beam 100′ to an ion source 3′, and the gauge head is used while being connected to a vacuum device (not shown). Further, the ion source 3′ of FIG. 18 is controlled by a controller 200′. The ion beam captured by the ion collector 40′ is measured as a current I with an ammeter 201′, the current I is converted into a pressure P by an arithmetic circuit 202′, and then the pressure is displayed on a display device 203′.
Furthermore, in the case of the gauge head of the extractor vacuum gauge shown in FIG. 19, the ion collector 40′ is of a needle type in many cases.
The entire part including the electronic circuit is called a vacuum measurement device 1′, and FIG. 18 is an example of the ionization vacuum gauge. Further, in FIG. 19, when a quadrupole electrode or a magnetic deflecting mass spectrometer (not shown) is disposed between the ion collector 40′ and the ion extractor 30′ of the ion source 3′, a different vacuum measurement device such as a mass spectrometer or a helium leak detector may be provided.
The conventional ion source 3′ shown in FIG. 19 is disposed inside a pipe-shaped vacuum vessel 8′ connected to a vacuum device (not shown) in a communication state. In the conventional grid 10′ constituting the ion source 3′, a cylindrical top surface portion B is blocked by a wire net, and a bottom surface C is opened without being blocked by the wire net. Although the ion extractor 30′ having a small hole opened at the center thereof is disposed outside the bottom surface C of the grid 10′ (at the underside of the Z axis), the potential of the electrode is generally is set to a ground potential (0 V). For this reason, the electrode is continuously formed with the pipe-shaped vacuum vessel 8′ in many cases (Patent Document 1).